4-Alkoxy and 4-aryloxy-1,1,1-trifluorobut-3-en-2-ones of formula (I) are important synthetic intermediates for the preparation of fluorinated heterocycles.
2-Trifluoromethylpyridines and 6-trifluoromethylpyridine-3-carboxylic acid derivatives are intermediates for the preparation of biologically active compounds. For instance, WO 00/39094 A1 discloses trifluoromethylpyridine as herbicides, WO 2006/059103 A2 discloses trifluoromethylpyridines as intermediates in the production of pharmaceutical, chemical and agro-chemical products, WO 2008/013414 A1 discloses trifluoromethylpyridines as vanilloid receptor antagonists and WO 2012/061926 A1 describes trifluoromethylpyridines as calcium channel blockers.
WO 2005/026149 A, DE 24 29 674 A and EP 51 209 A disclose certain precursors used in instant invention.
The common route for the preparation of 6-trifluoromethylpyridine-3-carboxylic acid derivatives was first reported by Okada et al., Heterocycles 1997, 46, 129-132, and has only been slightly modified by others. The common synthetic strategies are summarized in Scheme 1:

This route has disadvantages for the large scale production of 6-trifluoromethylpyridine-3-carboxylic acid derivatives, because ethylvinylether is highly flammable and therefore difficult to handle, and because the trifluoroacetylated enolether and the trifluoroacetylated enamine intermediates are unstable and cannot be stored for a longer time. Moreover, most vinyl ethers are mutagenic.
US 20130079377 describes the use and preparation from vinyl ethers of 4-alkoxy-1,1,1-trifluorobut-3-en-2-ones for the synthesis of novel vanilloid receptor ligands.
US 20120101305 discloses the preparation of 4-alkoxy-1,1,1-trifluorobut-3-en-2-ones from vinyl ethers and trifluoroacetyl chloride.
US 20140051892 A1 discloses a method for the preparation of 4-ethoxy-1,1,1-trifluorobut-3-en-2-one by reacting trifluoroacetyl chloride with ethyl vinyl ether, followed by thermolysis of the resulting chlorinated intermediate. A disadvantage of this method is the formation of hydrogen chloride, which is corrosive and could lead to a product of low storability.
WO 2004/078729 A1 discloses the preparation of compound of formula (Xa) from inter alia 4-alkoxy-1,1,1-trifluorobut-3-en-2-ones;
and discloses on page 18 in example P2 the use of 4-ethoxy-1,1,1-trifluorobut-3-en-2-one for the preparation of compound of formula (X-1).

Compound of formula (Xa) and compound of formula (X-1) are intermediates for the preparation of herbicides.
All known routes to 4-alkoxy-1,1,1-trifluorobut-3-en-2-ones are based on the reaction of vinyl ethers with trifluoroacetyl chloride or trifluoroacetic anhydride, whereupon one equivalent of HCl or trifluoroacetic acid are formed as byproducts, that must usually be trapped by addition of a base to prevent the acid-mediated degradation of the product. A further disadvantage of this synthetic strategy for the large scale production of 4-alkoxy-1,1,1-trifluorobut-3-en-2-ones is the high flammability and mutagenicity of vinyl ethers.
There was a need for an improved method for the preparation of 4-alkoxy-1,1,1-trifluorobut-3-en-2-ones. The method should not require the use of the problematic trifluoroacetyl chloride and ethylvinylether. This need was met by the method of instant invention as outlined below.
Compared to prior art, the method of the instant invention offers several advantages: It gives access to 4-alkoxy-1,1,1-trifluorobut-3-en-2-ones without the formation of hydrogen chloride. Only acetic acid, ethyl acetate, and ethyl formate are formed as byproducts, allowing the use of non-HCl-resistant reactors. Importantly, no problematic vinyl ethers are required. Moreover, the method of the present invention only comprises one synthetic step, and is therefore less costly than the two-step procedure disclosed in US 20140051892 A1.
In the following text, if not otherwise stated,    ambient pressure usually 1 bar, depending on the weather;    halogen means F, Cl, Br or I, preferably Cl, Br or I;    alkyl means a linear or branched alkyl, examples of alkyl include methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, tert-butyl, pentyl, hexyl, heptyl and the like;    cyclic alkyl or cyclo alkyl include cyclo aliphatic, bicyclo aliphatic and tricycle aliphatic residues; examples of “cycloalkyl” include cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, norbornyl and adamantyl;    alkoxy means alkyl-O, i.e. the radical obtained by removal of the oxygen-bound hydrogen from an aliphatic alcohol;    (alkoxy)alkoxy refers to alkoxy groups, in which the alkyl group is substituted with one additional alkoxy group; examples of (alkoxy)alkoxy include methoxymethoxy with formula MeO—CH2—O—, 2-(methoxy)ethoxy with formula MeO—CH2—CH2—O— and 2-(cyclopropylmethoxy)ethoxy with formula (C3H5)CH2—O—CH2—CH2—O—;    Ac acetyl;    tBu tertiary butyl;    cyanuric acid chloride 2,4,6-trichloro-1,3,5-triazine    DBU 1,8-diazabicyclo[5.4.0]undec-7-ene;    DABCO 1,4-diazabicyclo[2.2.2]octane;    DMF N,N-dimethylformamide;    DMA N,N-dimethylacetamide;    DMSO dimethylsulfoxide;    halogen means F, Cl, Br or J, preferably F, Cl or Br;    hemiacetal refers to the adduct of an alcohol, for instance methanol or ethanol, with a ketone or with an aldehyde; a hemiacetal may also result upon the addition of water to an enol ether; for instance, the hemiacetal of methanol with 1,1,1-trifluoroacetone is F3C—C(OH)(OCH3)—CH3;    hexanes mixture of isomeric hexanes;    hydrate refers to the adduct of water with a ketone or with an aldehyde, for instance, the hydrate of 1,1,1-trifluoroacetone is F3C—C(OH)2—CH3;    LDA Lithium diisopropyl amide    NMP N-methyl-2-pyrrolidone;    sulfamic acid HO—SO2—NH2;    Temp Temperature;    TriFA 1,1,1-trifluoroacetone;    THF tetrahydrofuran;    trifluoroacetone 1,1,1-trifluoropropan-2-one;    xylene 1,2-dimethylbenzene, 1,3-dimethylbenzene, 1,4-dimethylbenzene or a mixture thereof.